Numerical Ideal MHD Modeling of the Kink Double-Gradient Magnetic Instability
Abstract
The kink mode of the ideal MHD instability developing in the magnetotail-like magnetic configuration with tailward-growing normal magnetic component is studied by means of linearized 2-dimensional and non-linear 3-dimensional MHD modeling. While generally the instability of such kind is known as 'ballooning instability', this term implies usually the oblique propagation and background configuration with strong normal magnetic component. However, we consider the particular case of the transversal wave vector and weak normal magnetic component (small radius of the magnetic field line curvature), which configuration is favorable to the special branch of ballooning instability known as 'double-gradient' mode, introduced recently to describe the magnetotail flapping oscillations. The initial equilibrium for our numerical simulations is fixed by the solution of the Grad-Shafranov equation obtained in the frame of the tail approximation. The results of the 2d linearized MHD code agree with the analytical predictions, and the growth rate is found to be close to the peak value provided by an analytical estimate. The analytical solutions for the perturbations of magnetic and velocity components (eigenfunctions) are also confirmed. The 3D calculations show that the double-gradient mode is excited in a region of large curvature of the magnetic field lines. The overall growth rate is found to be close to the theoretical estimate averaged over the computational domain.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMSM11A2075K
- Keywords:
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- 2744 MAGNETOSPHERIC PHYSICS Magnetotail;
- 2753 MAGNETOSPHERIC PHYSICS Numerical modeling;
- 2752 MAGNETOSPHERIC PHYSICS MHD waves and instabilities;
- 2772 MAGNETOSPHERIC PHYSICS Plasma waves and instabilities